Different lenses are used for the various filming conditions depending on the application. Lenses are routinely continuously changed on the film camera during filming. Lenses can have three adjustment axes: focus, aperture, and zoom adjustment axes. Each adjustment axis has a scale, which is provided with engraved values by the lens producer. A marking indicates the currently set value.
Flanging servomotors onto the pinion of the adjustment axis on the lens is known for focusing on a motif, or for setting the aperture or the zoom region of film cameras. The activation of the individual servomotors is performed via a focusing unit, which is often embodied as a separate device. However, the focusing unit can also be integrated in the servomotor. It is also the case that the servomotor and/or the focusing unit are integrated in the lens, or are fastened as a joint unit on the lens.
It is possible for the operator to predefine setpoint positions of the focusing unit with the aid of one or more manual control units. The devices are connected via cable or radio connections. Finally, the servomotor processes the preset and adjusts the graduated ring on the lens.
Manual control unit, focusing unit, and servomotor form the lens control system of a film camera.
In the case of the recording of films, in particular the correct focusing of the film camera is a critical task. In particular in the case of artistically worthwhile films, a low depth of field is very often used, in order to emphasize specific objects or persons or the parts thereof accordingly. It is prior art that the lens control system can be assisted by further auxiliary devices especially during the focusing.
One possibility for focusing is, for example, is to aim at the object to be focused using a laser-based distance meter or an ultrasonic measuring device and to obtain the focusing information for the film camera therefrom. This has the disadvantage that in the case of moving objects, continuous tracking is necessary and in many cases the spatial relationship between film camera and distance meter is also not unambiguous. A further disadvantage is that these measuring devices only measure the distance from one specific point in space.
The data must be exchanged between these individual devices. In the case of rapidly moving objects, there is a trailing effect of the focus motor, since a large amount of time delay occurs due to the data exchange and the separate processing of data. Following very rapid objects is thus not possible.
A method and a device for focusing a film camera are known from EP 1 084 437 B, in which auxiliary cameras are used, which are provided laterally adjacent to the actual film camera. These auxiliary cameras are arranged so they are pivotable, so that the optical axes can be aligned onto the object to be focused. By triangulation, the distance to this object is calculated and the signal for the focusing is obtained. This system has the disadvantage that the mechanical movement of the auxiliary camera is susceptible to failure and even slight tolerances in the pivot movement, in particular in the moderate distance region, can result in large irregularities in the distance determination. In the event of a lens change, the system is to be recalibrated.
The above problems are partially solved by the use of a camera as described in WO 2009/133095 A. An auxiliary representation, which can be used to obtain items of distance information, is generated by an auxiliary sensor attached to a camera. However, this has the disadvantage that it is not readily possible to perform a distance measurement before a recording without using the camera, and the distance measurement is always dependent on the respective lens used, which is fitted on the camera. The calibration of the distance measurement is also only possible with the camera in the respective present state in the case of the known solution.
Independently of the fact that the lens must be changed very often in the case of film cameras, the following problem exists: real optics for film cameras pump, i.e., the image detail (the focal length) changes during focusing, a constant relationship of the image details is thus not provided between the two cameras. To calculate a depth image, however, the imaging scales and therefore the image details of all participating cameras are to be known precisely. In the case of zoom optics, the general problem exists of knowing the current precise focal length region. Most optics for film cameras do not have installed electronics, which output the scale setting and the focal length region.
A further problem is that real optics for film cameras, above all zoom optics, change the optical axis during zooming, or change the optical axis as a function of how the optic is installed on the camera. Therefore, a parallel alignment of the optical axes is only possible in reality by way of a very high level of effort, since the entire camera (camera including optic) must be moved during zooming. These two deviations (pumping and traveling of the optical axis) would have to be predefined by an algorithm for depth calculation and are different in every optic. The measurement is imprecise or is not even possible without these values.
However, the greatest problem during filming is the following: film recordings often have a low desired depth of field. In essence, the imaging of the main camera is fuzzy in large subregions. A depth calculation cannot occur in fuzzy image regions, i.e., the main camera can only be used for calculating a stereoscopic imaging if the depth of field is very large.
A less relevant, but nonetheless often interfering effect is that color images are less suitable for a depth calculation (above all, one which is to be executed in real time) and deliver comparatively imprecise results. Therefore, images from grayscale cameras are preferably used for the depth calculations.